This section provides the reader with a brief background of technology in the context of embodiments of this disclosure. Not only does this section provide context for several shortcomings in prior technology, but it also provides context about how the prior technology could, and will, benefit from various techniques described here. Simply because information appears in this section should not be taken as indicating its presence in the prior art. To the contrary, and as described immediately above, this section also provides context for certain significant improvements described and claimed in this disclosure.
Often specific survey objectives cannot be met by applying only one geophysical method. For example, in seismic and sonic reflection surveys, seismic refraction lines provide important information about velocities of near-surface materials which make it possible to apply needed corrections to reflection travel times. As electrical resistivity surveys depend on different physical properties than seismic or sonic surveys, the two taken together can provide important cross checks. If a system could perform multiple survey methods, better information about, for instance, the shallow subsurface could be obtained with a single multi-method survey.
Furthermore, there is developing interest in repeating surveys to observe changes that may occur in the subsurface, such as seasonal changes in groundwater level, effectiveness of subsurface pollutant remedial activities, and soil movement and water penetration under roadways, bridges, and dams. This usually requires that equipment be in place for long periods of time and necessitates frequent visits to the survey sites by geophysical technicians to monitor changing subsurface conditions.
The present state of the art does not provide an effective way to remotely manage field equipment and monitor survey data, much less monitor data in real-time. Field personnel must travel to the sites, perform the survey, collect the data in a temporary data storage device, and carry the data to a data center for processing and analysis. This may be done monthly, weekly, or more frequently depending upon how quickly the subsurface feature being monitored changes.
During a survey, one may discover that equipment performance has degraded or some components are not performing at all. Presently, he or she must then contact a service technician by telephone to report the problem, resulting in lengthy and sometimes confusing attempts to diagnose the problem and repair the equipment. The result is that the service technician must travel to the site to diagnose the problem, or the equipment must be sent to a service center for diagnosis and service.
Often, when equipment is returned to a service center, the equipment is found to be in satisfactory condition, and the problem remains at the site. This results in excessive “down-time” in the field and unplanned and excessive costs. If a means to remotely manage survey equipment and collect survey data were incorporated into a survey system, significant operational and cost advantages would accrue. For example, electrical resistivity strategies could be changed remotely and interactively from Dipole-Dipole to Wenner/Leed by the investigator. Measurement parameters such as injection current magnitude and period, survey frequency and method could be changed. Remote tests and diagnostics could be performed on all equipment to determine their level of operability and specific equipment requiring service.
A further disadvantage of present survey systems, in particular systems for the electrical resistivity, is the lengthy time required to perform a typical survey. Time limitations are due primarily to internal instrument noise caused by conductive coupling between cable conductors and connector pins (signal to noise ratio). The number of receivers active during a survey event is currently limited by the number of conductors in a cable. If a system were to eliminate the coupling noise and to remove the limitations on the number of receivers, shorter survey times could be achieved-from hours to minutes for a typical 100-survey probe system. This could result in survey crew labor savings and overall greater productivity.
Present electrical resistivity survey systems require multi-conductor cabling to simultaneously carry high voltage and low level analog potential signals. Multiple cable segments with integrated survey probes are connected together in the field in preparation for surveys. The cable segments must be connected with very careful attention to the order in which they are connected. Whether passive survey probes or intelligent survey probes, incorrect connections result in unintelligible and useless data. If an electrical resistivity survey system did not require cables to simultaneously carry high voltage and low voltage signals, data accuracy would be improved. Cables could be lighter and easier to handle in the field. Furthermore, if it were not required that cable sections must be connected in specific order, connection errors, survey errors, and field set-up time could be reduced.
Further, if data and control information could be exchanged between survey probes and the survey controller(s) by modulated radio waves a further reduction in cable wiring could be achieved.
Additionally, with the proper radio design, radio receivers associated with each probe could triangulate relative position relative to one or more transmitters and provide precise position location of each survey probe relative to one or more transmitters whose positions are accurately known. Furthermore, knowing the precise locations of each survey probe, each survey probe can be assigned an address based upon it's serial number and it's spatial position. The particular cable segment to which it is connected is not relevant.
Shortcomings mentioned above are not intended to be exhaustive but rather are among many that demonstrate that room for significant improvement remains in the art and that the techniques of this disclosure would be useful and beneficial.